The agency recently OK’d the application from the St. Louis 9/11 Questions Meetup Group under the Adopt-A-Highway program. The approval means the group will have two signs bearing their names erected next month on each end of a half-mile stretch of Olive Boulevard east of Lindbergh Road in the St. Louis area.

In return, the group agrees to pick up litter along the stretch at least four times a year for the next three years.

Some members of the St. Louis 9/11 Questions Meetup Group suggest that the U.S. government may have been involved in the 9/11 terrorist attacks. Here's how the group describes itself on its website:

“We are residents of the Greater St. Louis Area (and other areas) concerned about the many disturbing aspects of the 9/11 attacks and interested in finding out more about those events. We have many disagreements, but we agree that 9/11 is worth inquiring into.”

Holly Dentner, a state Transportation Department spokeswoman, said the state can’t turn away a group’s Adopt-A-Highway application based on the group’s viewpoints. As long as the applicant fulfills the program’s obligations, which include collecting litter at least four times a year and submitting an activity report to the state, it can participate, she said.

“We can’t deny an adopter group a section of highway to pick up trash just based on their belief or opinions,” she told NBC News. “Should they not fulfill the obligations, we can cancel and remove the signs.”

A federal appeals court ruling in 2000 limited Missouri’s ability to pick and choose highway “adopters.” The 8th Circuit Court of Appeals upheld a federal judge’s ruling that Missouri could not reject the Ku Klux Klan’s application to adopt a stretch of Interstate 55 south of St. Louis. The Missouri Legislature later voted to name the stretch of highway in question the “Rosa Parks Highway,” in honor of the black civil rights activist from Alabama. The KKK was eventually dropped from the Adopt-A-Highway program for failing to pick up litter.

Other states have had Adopt-A-Highway controversies as well. In Georgia, a KKK chapter sued in September after the state rejected the white supremacist group’s application. In 2005, the American Nazi Party adopted a stretch of rural highway outside Salem, Ore., but their signs were quickly vandalized and later removed.

Dentner said the St. Louis 9/11 Questions group is among more than 4,000 adopter groups who pick up a total of about 20,000 bags of trash along 6,463 miles of roads across the state a year.

The program saves the state at least $1 million a year in trash collection costs, said Tom Blair, assistant district engineer for state Transportation Department in St. Louis. “Without the Adopt-A-Highway program, all roadsides in Missouri would be much dirtier,” he said.

Donald Stahl, organizer of the St. Louis 9/11 Questions Meetup Group, believes the World Trade Center towers did not collapse strictly as a result of being struck by airplanes hijacked by terrorists. He says they may have been brought down by a controlled demolition.

As for why his group wants to adopt a highway: “Like all the other groups that do it, we like the free publicity,” he told KSDK.

Stahl did not respond to an email request from NBC News for comment.

The group’s philosophy doesn’t sit well with Warren Nelson, of the St. Louis suburb of Kirkwood. He and his wife lost their son, David Nelson, in the Sept. 11 attacks.

“Certainly we would not be in agreement with an organization that believes that our U.S. government had anything to do at all with 9/11,” he said. “No way.”

As to highway signs bearing the group’s name, Nelson said: “I would not want to drive down and see a sign like that.”